[P-CG20] Future missions and instrumentation for space and planetary science

[PCG20-P15] Development of compact Langmuir probe payload based on microsatellite platform

*Jin Wang¹, Qinghe Zhang¹, Qingfu Du², Duan Zhang¹ (1.National Space Science Center, CAS, 2.Shandong University)

Keywords:Langmuir probe, Ionosphere in-situ detection, Plasma diagnosis

The ionosphere is a region of the Earth's atmosphere that is partially ionized by solar radiation. It is an important link in the sun-to-Earth energy transmission chain, a key component of space weather, and the region of Earth's space closest to the application level of space physics. However, the state of the ionosphere is complex and changeable, and there are many inhomogeneous structures of different scales, which can affect high-tech applications such as radio communications, navigation and positioning, and remote sensing detection. The main characteristics of these inhomogeneities are uneven plasma density, spatial scales ranging from centimeters to kilometers, and strong randomness, making it difficult to accurately "capture" them. In order to detect the ionospheric plasma density, many ground-based and space-based detection methods have been developed internationally. The most common space-based detection method is the Langmuir Probe (LP) carried by satellites to achieve in-situ detection. However, due to the limited number of satellite platforms and insufficient spatiotemporal resolution of existing Langmuir probe payloads, precise monitoring of these non-uniform bodies of different scales is insufficient, mechanism understanding is not thorough, and modeling and forecasting are inaccurate, making it difficult to effectively ensure the safety of high-tech systems such as communication and navigation. In this study, our team designed and developed a high spatial resolution Langmuir probe payload that can finely detect sub meter level plasma structures. The overall payload adopts a miniaturized design, equipped with four cylindrical Langmuir probes (25 mm long and 0.5 mm diameter); The electronic system adopts a universal interface design, with a power consumption of less than 2.5 W and an overall weight of less than 1.5 kg. It also has up to 32 GB of data storage space, making it particularly suitable for carrying small satellite platforms for precise ionospheric detection. The payload adopts a four probe working mode, which can achieve multiple working states and can detect in-situ parameters such as electron density (Ne), electron temperature (Te), and plasma potential (Vp) of ionospheric plasma with high spatial resolution. Under normal operating conditions, one probe of the payload is in scanning mode to obtain plasma parameters such as Te and Vp, while the other three probes are in fixed bias voltage fast sampling mode to obtain high spatial resolution Ne data. The sampling rate and filter ratio of all channels can be modified in orbit. In addition, due to the fact that miniature cylindrical probe sensors can collect very few ions and electrons, the signal collected by the probe is very weak, and the probe signal shows exponential growth and rapid changes in the transition region of the I-V characteristic curve. This paper studies the characteristics of probe signal acquisition and innovatively proposes a nonlinear signal processing method for micro probes. The weak probe signal is logarithmically amplified at the analog circuit end, improving the signal-to-noise ratio of weak signal acquisition while considering the dynamic range of acquisition. The payload has passed environmental testing experiments such as vacuum thermal cycling and sinusoidal and random vibrations, and calibration experiments have been conducted in various density ranges in a space plasma simulation vacuum chamber. The results show that the compact Langmuir probe payload can work normally in the space environment and can also achieve high spatial resolution diagnosis of plasma in the density range of 10⁸~10¹³ m^-3, which fully meets the requirements of ionospheric plasma detection. The designed lifespan of the payload is two years. It has recently been launched into space with a small satellite weighing 30 kilograms, operating in a low Earth orbit at a distance of 530 km. The payload is currently in good working condition and preliminary detection data has been obtained. If this payload can be widely applied and promoted, it will greatly promote the development of ionospheric fine detection, research, and modeling, serving the space weather forecasting industry in China.